1. Field of the Invention
The present invention relates to core-drilling apparatus, and in particular, to a roof core-drilling apparatus and drilling guide adapted to be used in combination with a rotary drive, in which the mandrel portion of the invention operates not only for mechanically connecting the saw body to the drive means during the drilling operation, but also as a plunger for ejecting the care of the work material from the saw cup when the drilling operation is completed.
2. Description of the Related Art
Although core cutters are well known in the prior art, core cutters specifically adapted for use in the cutting of roof cores over a few inches in length in combination with drill motors are not so well known. In hole saw operations where the core removed is less than several inches in length, saw cups with pilot bits are normally used in conjunction with a power drill. The problem faced by all core drilling devices has been the difficulty in ejecting the work material after completion of the drilling operation. When the saw cup has penetrated a distance of an inch or more, a cylindrically-shaped core of work material becomes lodged tightly within the saw cup, and in prior art hole, was difficult to remove.
Several core-drilling devices are known in which the core of the work material is ejected from the saw cup at the completion of the drilling operation. In U.S. Pat. Nos. 5,435,672, 5,690,452, and 5,934,835 a spring biases the core as the hole is being cut and automatically ejects the core from the saw after completion of the drilling operation.
The problem with these spring-loaded hole saws is the uncertainty of whether the spring bias will be sufficient to eject the core. Independent of the effect of time and weather on the properties of the spring material, different work material requires a different amount of force necessary to eject the core, and a work material of particularly “sticky” material would invariably leave the core stuck in the saw. This problem has been addressed in U.S. Pat. Nos. U.S. 5,082,403, 5,096,341 and 5,435,672, in which the mandrel-forming portion of the hole saw is threadedly received by the base of the saw cup and by rotating the mandrel in reverse of the normal drilling operation direction, the core is ejected from the saw cup. Differences in these inventions being adapted to either left-hand threaded or right-hand threaded arbor-receiving bores. U.S. Pat. No. 6,341,925 responded to a need for a plug ejecting hole saw which utilized a thin base wall and thus was not adaptable to a threaded base, however still used a threaded mandrel and a complex spring biased attachment bore. U.S. Patent Application U.S. 2002/0131835A1 is a further refinement of the '925 patent, in which hole saw cups of various diameters and having different sized attachment bores may readily be interchangeably mounted on a single-ended arbor-holder by a twisting, snapping action.
The prior art addressing roof core cutters has concentrated on manual core drilling apparatus. The Red Dragon CC 501 Core Cutter made and sold by Flame Engineering is such a manual core cutter capable of extracting a 2 inch diameter by 7 inch sample. Not adapted to be used in conjunction with a drill motor, the 501 Core Cutter is turned by hand.
The problem of adapting manual roof core cutters to operate with a drill motor has not been adequately addressed. Not having a pilot bit to guide the saw at the beginning of the operation, a drill motor would be difficult to use safely. In addition, the torque generated by a general purpose drill motor may be insufficient to overcome the binding resistance generated by several inches core material. None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a roof core cutter solving the aforementioned problems is desired.